The present invention is directed to human powered vehicles and, more particularly, to a variable speed generator for a human powered vehicle such as a bicycle.
A generator contained within a wheel hub, typically called a hub dynamo, frequently is fitted to a bicycle. Such a hub dynamo is disclosed in Japanese Patent Publication No. 6-88544. The disclosed dynamo comprises a hub shaft, a hub shell rotatably mounted around the hub shaft, a transmission mechanism that increases the rotational speed of the hub shell to an output member, and a power generating mechanism that has a magnet connected to the output member and a coil fitted to the hub shaft. In such a hub dynamo, the magnet rotates faster than the hub shell so that power generation is high even at low wheel speeds. However, when wheel speed is high, the dynamo may produce excessive voltage and cause malfunction or destruction of electrical components, such as lamps powered by the dynamo, unless special protective circuitry is added to the system.